This invention claims priority of the German patent application 100 48 724.6 which is incorporated by reference herein.
The invention concerns a device for stretching cryostatic sections.
In cryostats, thin sections of frozen specimens are produced with a microtome and are then mounted on a specimen slide and examined with a microscope. As the frozen specimens are sectioned, the difficulty exists that the frozen specimens curl up during sectioning. These curled-up specimens are very difficult to mount on a specimen slide, and the risk additionally exists of breaking the specimens. Section stretching devices are used to prevent the undesirable curling. These section stretchers have a glass or plexiglas plate that is arranged on the knife back, parallel to and at a short distance from the knife edge, in such a way that a thin gap is created between the knife back and the plate. During sectioning, the sectioned specimen slides into the gap between the plate and the knife back.
After sectioning, the section stretcher is taken off the knife back and the sectioned specimen is removed from the knife back. This removal is accomplished by the fact that a specimen slide, warmed to room temperature, is set on the knife edge and slowly lowered onto the sectioned specimen. Upon contact, the ice in the specimen abruptly thaws and the sectioned specimen adheres to the specimen slide.
DE 20 28 898 C3 discloses and describes a section stretcher of this kind in a cryostat. The plate of the section stretcher is arranged parallel to the knife back by way of a lever device having a motorized drive. The section stretcher is in this case a constituent of an automatic section removing system with specimen slides. The material of which the plate of the section stretcher is made and the manner in which the gap between the knife back and the plate of the section stretcher is formed are, however, left undefined in this document. The full disclosure of DE 20 28 898 C3 is hereby incorporated by reference.
DE 25 06 255 B2 discloses an ultramicrotome having a section stretcher in which the plate of the section stretcher is formed from the countermember of a broken triangular glass knife. Broken triangular glass knives are, however, used exclusively in ultramicrotomy and are unsuitable for larger specimens. The full disclosure of DE 25 06 255 B2 is hereby incorporated by reference.
The document xe2x80x9cLEITZ 1720 Cryostat, catalog no. 913 039, Ernst Leitz Wetzlar GmbH, July 1982xe2x80x9d depicts a cryostat having a section stretcher in which the plate of the section stretcher is configured as a one-piece injection-molded plexiglas plastic part having webs shaped onto both ends. The requisite gap between the plexiglas plate and the knife back is defined by the shaped-on webs. The webs shaped onto both ends are present in this case on both the front side and the rear side of the plexiglas plate, so the plate is usable from both sides. The use of plexiglas has the advantage that the component is easy to manufacture as an injection-molded part, and the finished part can moreover easily be machined by drilling, milling, and the like. It is disadvantageous, however, that the plastic part is easily scratched and that static charging takes place to a certain extent. The plexiglas moreover has poor chemical resistance. Since it is necessary to work with solvents in the vicinity of the sectioning knife for cleaning purposes, the risk exists that the plate will lose its transparency and thus become unusable. The full disclosure of this document is hereby incorporated by reference.
Section stretchers having glass plates are also known. Here the necessary webs are configured as glass strips and are mounted on the glass plate with a suitable adhesive. This method is very laborious, however, since the glass must be carefully cleaned before adhesive bonding. Since the gap between the knife back and plate is about 0.15 mm, the glass webs are correspondingly delicate and can easily break off when set onto the steel knife in the microtome. Glass webs of nonuniform thickness, however, result in an xe2x80x9cobliquexe2x80x9d gap between the knife and glass plate and are therefore unusable.
In a further development of these section stretchers, a multi-layer baked enamel has been applied onto the glass plate instead of the adhesively bonded glass webs. This has the disadvantage, however, that the permissible tolerance for the gap, which is approximately 0.15 mm in thickness, can only insufficiently be maintained. A further disadvantage lies in the fact that the hardened enamel is very brittle and thus, as in the case of the adhesively bonded glass strips, easily chips off when set onto the steel microtome knife.
It is therefore the object of the present invention, proceeding from the known existing art, to configure a section stretcher in a more robust fashion and also to ensure easy replaceability of the plate. These and other advantages will be clear to one skilled in the art.
The present invention provides for a device for stretching cryostatic sections, comprising: a sectioning knife; a plate arranged on a back side of the knife so that a gap for receiving the cryostatic section is formed between the plate and the back of the knife; a frame, open in a direction of an edge of the knife, for receiving the plate; and webs internally located and shaped on the frame and having support surfaces to support the plate, wherein the frame includes a contact rim for setting the frame onto the back of the knife, and wherein a height difference between the contact rim and the support surfaces defines a dimension of the gap. The frame may be of one-piece configuration, and its shape may be of a rectangle or a triangle. The plate may be made of glass or plastic, and may be detachably secured to the frame by two screws arranged on the frame. Further, the webs may be provided on at least two limbs of the frame.